Integrated circuit with channel estimation module and method therefor

ABSTRACT

An integrated circuit comprises channel estimation module for generating at least one channel estimation signal based on at least one of a plurality of pilot signals within concurrent resource elements. The channel estimation module comprising extension module arranged to receive a demodulation reference signal comprises the plurality of pilot signals and to add an extension to the demodulation reference signal, inverse discrete Fourier transform (IDFT) module arranged to perform an inverse discrete Fourier transform function on the extended demodulation reference signal to generate a time domain reference signal, reference signal separation module arranged to separate out at least one pilot signal component from the time domain reference signal. The channel estimation module further comprises and discrete Fourier transform (DFT) module arranged to perform a discrete Fourier transform function on the at least one pilot signal component to generate at least one extended channel estimation signal.

FIELD OF THE INVENTION

The field of this invention relates to an integrated circuit comprisingchannel estimation module, and a method therefor, for generating atleast one channel estimation signal. In particular, the field of theinvention relates to an integrated circuit comprising channel estimationmodule, and a method therefor, for generating at least one channelestimation signal based on at least one of a plurality of pilot signalswithin concurrent resource elements.

BACKGROUND OF THE INVENTION

In wireless transmission systems such as orthogonal frequency divisionmultiplexed (OFDM) and orthogonal frequency division multiple access(OFDMA) transmission systems, as well as single-carrier frequencydivision multiple access (SC-FDMA) transmission systems, an availablecarrier frequency band is divided into multiple smaller sub-carrierfrequency bands. Multiple signals may then be modulated onto thesesub-carrier frequency bands and simultaneously transmitted over theavailable carrier frequency band.

Ideally, the signal received by a receiver matches the transmittedsignal. However, in real communication channels, such as a wirelesstransmission channels, the received signal will vary based on theparticular propagation properties of the communication channel, such asthe presence of signal interference and multipath reflections.Accordingly, in many OFDM systems, the receiver will perform a channelestimation process to determine the effect that the channel has on areceived signal. From such a channel estimation, the receiver is thenable to determine how to compensate the received signal for channelfading etc. in order to retrieve the proper shape of the originallytransmitted signal.

One way in which this channel estimation may be accomplished is for thereceiver to know in advance the ‘modulation’ shape of at least part of atransmitted signal. However, transmitted data is typically random andunpredictable, and so is not suitable for this purpose. One solution isto embed a known symbol pattern (often referred to as a pilot sequence)into the transmitted signal. In this manner, by examining the effect ofthe channel on this embedded known symbol pattern within the receivedsignal, the receiver may be able to estimate an effect of thecommunication channel on the rest of the received signal, therebyallowing it to determine how to compensate for the communication channeleffect.

FIG. 1 illustrates an example of a block diagram of a known channelestimation circuit 100 for an OFDM receiver. The channel estimationcircuit 100 receives as an input a demodulation reference signal (DMRS)110 comprising a pilot signal in a form of a known reference symbolmodulated onto a sub-carrier signal. IDFT circuitry 120 transforms themodulated DMRS signal 110 into the time domain. Filter circuitry 130then performs a filtering operation on the time domain signal to filterout noise from the pilot signal, and thereby improve the accuracy of thechannel estimation signal. DFT circuitry 140 then transforms thefiltered time domain signal back into the frequency domain to generate achannel estimation signal 150.

A problem with performing such DFT based channel estimation on a pilotsequence is an effect known as the “edge effect”, whereby afterfiltering is performed in the time domain, for example by the filtercircuitry 130, when the signal is transformed back into the frequencydomain using a DFT, for example by the DFT circuitry 140, the estimatedcommunication channel information exhibits high Mean Square Error (MSE)at the edges of the frequency domain signal. This undesirable phenomenonincreases with the allocation size. FIG. 2 illustrates an example of aplot of the MSE for a traditional frequency domain channel estimationapproach 210 and a plot of the MSE for a typical DFT-based channelestimation approach 220. As illustrated, whilst the DFT-based channelestimation approach 220 performs adequately within the central region ofthe allocation, the MSE at each edge of the plot for the DFT-basedchannel estimation approach 220 is very poor, and significantly worsethan that for the traditional frequency domain channel estimationapproach 210.

SUMMARY OF THE INVENTION

The present invention aims to provide an integrated circuit comprisingchannel estimation module, a communication unit comprising such channelestimation module and a method therefor as described in the accompanyingclaims.

Specific embodiments of the invention are set forth in the dependentclaims.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects and embodiments of the invention will bedescribed, by way of example only, with reference to the drawings.Elements in the figures are illustrated for simplicity and clarity andhave not necessarily been drawn to scale.

FIG. 1 illustrates an example of a block diagram of a known channelestimation circuit.

FIG. 2 illustrates an example of a plot of the Mean Square Error (MSE)for a typical discrete Fourier transform (DFT)-based channel estimationapproach.

FIG. 3 illustrates an example of a simplified block diagram of part of acommunication unit.

FIG. 4 illustrates a simplified block diagram of an example of atransmit chain module.

FIG. 5 illustrates a simplified block diagram of an example of areceived chain module.

FIG. 6 illustrates an example of an orthogonal frequency divisionmultiplexed (OFDM) transmission system.

FIG. 7 illustrates an example of resource grids representing resourceelements for the OFDM transmission system of FIG. 6.

FIG. 8 illustrates an example of a channel estimation module of FIG. 5.

FIG. 9 illustrates an example of an extension of a frequency domainsignal.

FIGS. 10 and 11 illustrate frequency domain views of pilot signalswithin a demodulation reference signal.

FIG. 12 illustrates an example of MSE plots for a traditional frequencydomain channel estimation approach, a traditional DFT based channelestimation approach and a DFT based channel estimation approach.

FIG. 13 illustrates an example of a simplified flowchart of a method forgenerating a channel estimation signal.

DETAILED DESCRIPTION

An example will now be described with reference to a wirelesscommunication unit, such as a base transceiver station, within awireless communication network. However, it will be appreciated that theexamples herein described are not limited to use within such acommunication unit, and may equally be applied to alternative devicesarranged to perform channel estimation within a communication systemsuch as, by way of example only, a mobile telephone handset, etc.Furthermore, because the example apparatus implementing the presentinvention is, for the most part, composed of electronic components andcircuits known to those skilled in the art, circuit details will not beexplained in any greater extent than that considered necessary asillustrated below, for the understanding and appreciation of theunderlying concepts of the invention and in order not to obfuscate ordistract from the teachings of the invention.

Referring to FIG. 3, there is illustrated an example of a simplifiedblock diagram of part of a communication unit 300. The communicationunit 300, in the context of the illustrated example, is a basetransceiver station comprising an antenna 302. As such, thecommunication unit 300 contains a variety of well known radio frequencycomponents or circuits 306, operably coupled to the antenna 302. Thecommunication unit 300 further comprises signal processing module 308,and an lub interface 322 for communication with, for example, a radionetwork controller (not shown).

For completeness, the signal processing module 308 is coupled to amemory element 316 that stores operating regimes, such asdecoding/encoding functions and the like and may be realised in avariety of technologies such as random access memory (RAM) (volatile),(non-volatile) read only memory (ROM), Flash memory or any combinationof these or other memory technologies. A timer 318 is typically coupledto the signal processing module 308 to control the timing of operationswithin the communication unit 300.

In accordance with some examples, the communication unit 300 is arrangedto operate within a frequency division system, and in particular anorthogonal frequency division multiplexing (OFDM) communication system.However, the communication unit 300 may be arranged to operate within acommunication system that uses an alternative modulation scheme, such asan orthogonal frequency division multiple access (OFDMA) communicationsystem or a single-carrier frequency division multiple access (SC-FDMA)communication system,

Referring now to FIG. 4, there is illustrated a simplified block diagramof an example of transmit chain module 400 for transmitting data within,say, an OFDM system. The transmit chain module 400 comprises a modulator410 arranged to receive bits to be transmitted 405, and to encode thosedata bits 405 into symbols. For example, the modulator 410 may bearranged to encode the data bits 405 using binary phase shift keying(BPSK), in which one bit is encoded to each symbol, quadrature phaseshift keying (QPSK), in which two bits are encoded to each symbol, or aquadrature amplitude modulation (QAM) scheme, in which multiple bits areencoded to each symbol. These data symbols are then output by themodulator 410 in the form of an encoded symbol stream 415 fortransmission. In addition to the data symbols, the modulator 410 furtherincludes within the encoded symbol stream for transmission pilot signalsas described in greater detail below. The encoded symbol stream 415 isthen provided to inverse fast Fourier transform (IFFT) module 420, whichperforms an inverse fast Fourier transform operation on the encodedsymbol stream 415, thereby converting it from the frequency domain tothe time domain to generate an encoded time domain signal fortransmission 425.

The time domain signal for transmission 425 is then provided to a cyclicprefix addition circuit 430, which adds a cyclic prefix to the beginningof each data slot. The addition of the cyclic prefix extends theeffective length of each data slot, thereby allowing multipath portionsof the subsequently received signal to settle before the next data slotis transmitted. As a result, inter-symbol interference (ISI) caused bymultipath interference may be substantially eliminated.

The extended time domain signal is then transmitted over the air byantenna 440. For example, the extended time domain signal may bemodulated onto an appropriate radio frequency (RF) carrier signal by RFmodulation circuitry (not shown) prior to being transmitted by antenna440. Additional/alternative moduleal elements may be included withintransmit chain module adapted to support alternative modulation schemes,such as DFT pre-coding module 450 in the case of, say, SC-FDMA.

Referring now to FIG. 5, there is illustrated a simplified block diagramof an example of receiver chain module 500 for receiving data within,say, an OFDM communication system, for example as may be implementedwithin the RF circuits 306 of the communication unit 300 of FIG. 3. Forthe illustrated example, at least part of the receive chain module 500forms a part of an integrated circuit 505.

An antenna 510 is arranged to receive a transmitted signal, for examplesuch as may be transmitted by transmit chain module 400 of FIG. 4, andto provide the received signal to the receive chain module 500. Thereceived signal typically may comprise one or more extended time domainsignals modulated on to RF sub-carrier signals. Accordingly, thereceived signal may be demodulated by RF demodulation circuitry (notshown) to retrieve the extended time domain signals, said extended timedomain signals then being provided to cyclic prefix removal module 520.

The cyclic prefix removal module 520 is arranged to remove a cyclicprefix added to the data slots within the received signal to retrieveencoded time domain signals 525. The encoded time domain signals 525 arethen provided to fast Fourier transform (FFT) module 530, which performsa fast Fourier transform operation on the encoded time domain signals525, thereby converting information within the signals from the timedomain to the frequency domain to generate encoded symbol streams 535.The received encoded symbol streams 535 are then provided to anequalizer 540, which extracts the encoded symbols within the encodedsymbol streams 535 to retrieve data bits encoded therein, and outputsthe retrieved data bits 545. By way of example, the data bits may beencoded within the encoded symbol stream 535 using binary phase shiftkeying (BPSK), in which one bit is encoded to each symbol, quadraturephase shift keying (QPSK), in which two bits are encoded to each symbol,or a quadrature amplitude modulation (QAM) scheme, in which multiplebits are encoded to each symbol. Additional and/or alternative logicalelements may be included within receive chain module adapted to supportalternative modulation schemes, such as IDFT module 580 and demodulator590 in the case of, say, SC-FDMA.

Within real systems the communication channel between a transmittingantenna and a receiving antenna comprises a fading nature, resulting indegradation and distortion of the amplitude and phase of data symbolswithin the received signals. In order to compensate for the fadingnature of the communication channel, known reference symbols, oftenreferred to as pilot signals, are included within the encoded symbolstream 415 by the modulator 410 within the transmit chain module 400.Accordingly, these known pilot signals are present within the encodedsymbol stream 535 received by the receive chain module 500. The valuesand placement of the pilot signals are known by both a transmittingdevice and a receiving device within a communication system. Forexample, the pilot signals may be based on a known reference symbolmultiplied by a known pilot sequence, such as a Zadoff-Chu or CAZAC(constant amplitude zero autocorrelation waveform) sequence. In thismanner, the receiving device has prior knowledge of at least a portionof the symbols within a received signal. The receiving device is thenable to use this prior knowledge of the pilot signals to determine animpulse response for the communication channel, and to compensate forthe fading nature of the communication channel in order to moreaccurately demodulate the encoded symbols within the received encodedsymbol stream 535.

Accordingly, the receive chain module of FIG. 5 further compriseschannel estimation module 560 for generating at least one channelestimation signal 570 based on at least one of a plurality of pilotsignals 550 within concurrent resource elements of received encodedsymbol streams 535, and to provide the at least one channel estimationsignal 570 to the equalizer 540. For example, a plurality oftransmitting devices may concurrently transmit pilot signals within acommon carrier frequency band, and the channel estimation module 560 maybe arranged to de-multiplex the pilot signals and to generate a channelestimation signal based on at least one of the de-multiplexed pilotsignals. The equalizer 540 is then able to use the channel estimationsignal(s) 570 to compensate for the fading nature of the respectivecommunication channel(s) in order to more accurately demodulate theencoded symbols within the respective received encoded symbol stream(s)535.

A problem with the use of such DFT and IDFT circuits is the “edgeeffect”, whereby channel estimations exhibit high Mean Square Error(MSE) values at the edges of their allocation. This problem is furthercomplicated by the multiple sub-carrier nature of OFDM transmissionsystems, where a receiving device may be required to perform channelestimation for a plurality of communication channels. In particular,with the evolution of current cellular networks that will allow fasterdata speeds and a new radio access technology that is optimized for IP(Internet Protocol) based traffic, technologies such as MIMO (SingleUser and Multiple User MIMO) have been introduced.

The Multiple Input Multiple Output (MIMO) systems increase transmissionchannel capacity by using multiple antennas in transmission and/orreception. Hence, different signals may be transmitted in the same bandof frequencies at the same time. Reference signals (for example pilotsignals), which may be transmitted to ease the detection process, mayeither be sent using different resource elements (for example asproposed for the 3^(rd) Generation Partnership Project (3GPP) Long TermEvolution (LTE) Downlink channel) or mapped onto the same resourceelements (for example as proposed for the 3GPP LTE Uplink channel, anexample of a structure for which is illustrated in FIG. 7).

FIG. 6 illustrates an example of, say, an OFDM transmission systemcomprising a base station (BS) 620 and a user equipment (UE) 610. The UE610 comprises multiple transmit chains (providing multiple inputs fortransmission channels) and the BS 620 comprises multiple receive chains(providing multiple outputs for transmission channels). Thus, togetherthe UE 610 and the BS 620 may be arranged to operate within a multipleinput multiple output (MIMO) arrangement in order to enhance linkrobustness and increase data rates, for example as proposed in the3^(rd) Generation Partnership Project (3GPP) Long Term Evolution (LTE)of the Universal Mobile Telecommunications System (UMTS). Accordingly,the UE 610 and BS 620 each comprise multiple antennae 612, 614, 622, 624and multiple transceiver circuits 616, 618, 626, 628 respectively, withonly two such antennae and circuits for each of the UE 610 and BS 620shown respectively for simplicity purposes only. Furthermore, the numberof transmit chains of the UE 610 need not match the number of receivechains of the BS 620. In order to successfully receive a MIMOtransmission, a receiver must determine the impulse response for thecommunication channel from each transmitting antenna.

For the dual antenna/circuit example illustrated in FIG. 6, for each ofan uplink and a downlink direction, there are a total of fourcommunication channels for which impulse responses are required to bedetermined. For alternative arrangements, such as where the UE 610and/or BS 620 comprise different numbers of antennae, a different numberof communication channels may be present. The example of FIG. 6illustrates the four uplink communication channels, for which there aretwo communication channels 630, 640 from the first antenna 612 of the UE610, one to each of the antennas 622, 624 of the BS 620, and twocommunication channels 650, 660 from the second antenna 614 of the UE610, also one to each of the antennas 622, 624 of the BS 620.

Referring now to FIG. 7 there are illustrated examples of a firstresource grid 710, representing resource elements for, for example, afirst transmit chain of UE 610 comprising transceiver circuit 616 andantenna 612 of FIG. 6, and a second resource grid 720, representingconsecutive resource elements for, for example, a second transmit chainof UE 610 comprising transceiver circuit 618 and antenna 614 of FIG. 6.For the illustrated example, the resource grids 710, 720 representresource elements for a single uplink transmission timeslot (T) 705.Each time slot within the transmission system bandwidth comprises N_(BW)_(—) _(sc) sub-carrier frequencies (illustrated at 725), which aredivided into resource blocks. Accordingly, within each resource grid710, 720 there is illustrated a resource block 735, the resource block735 comprising resource elements provided over N_(RB) _(—) _(sc)sub-carrier frequencies (which for the illustrated example comprisestwelve sub-carrier frequencies illustrated at 730). For the illustratedexample, the transmit chains of UE 610 are arranged to utilise MIMOtechnology, and as such the resource block 735 is allocated for use byboth the transmit chains of UE 610, and the transmit chains of UE 610are arranged to periodically transmit reference signals withinparticular resource elements within the resource block 735. Inparticular for the illustrated example, both transmit chains of UE 610are arranged to transmit reference signals within resource elements 760comprising a common time index (I=3) across all sub-carrier frequencies730 of the resource block 735. Accordingly, the two transmit chains ofUE 610 are arranged to transmit reference signals within the sameresource elements of the resource block 735.

Accordingly, and as illustrated in FIG. 6, the first antenna 612 of UE610 transmits a reference signal within each resource element 760comprising, say, a time index of I=3 across all sub-carrier frequencies730 for resource block 735 of timeslot 705. In this manner, each of thefirst receive chain of BS 620, comprising antenna 622 and transceivercircuit 626, and the second receive chain of BS 620, comprising antenna624 and transceiver circuit 628, receives via one of respectivecommunication channels 630, 640 the reference signal within resourceelements comprising a known time index from the first antenna 612 of UE610. Concurrently, the second antenna 614 of UE 610 also transmits areference signal within each resource element 760 comprising the timeindex of I=3 across all sub-carrier frequencies 730 for resource block735 of timeslot 705. In this manner, each of the first receive chain ofBS 620, comprising antenna 622 and transceiver circuit 626, and thesecond receive chain of BS 620, comprising antenna 624 and transceivercircuit 628, receives via one of respective communication channels 650,660 the reference signal within resource elements comprising the knowntime index from the second antenna 614 of UE 610.

Thus, as illustrated in FIGS. 6 and 7, each receiver chain of the BS 620receives reference signals from both of the transmit chains of the UE610 within concurrent resource elements. As a result, each receive chainis required to de-multiplex the channel taps in order to extract thedifferent reference signals.

Referring now to FIG. 8, there is illustrated an example of the channelestimation module 560 of FIG. 5. The channel estimation module 560comprises extension module 810 arranged to receive a demodulationreference signal (DMRS) 805, which for the example illustrated in FIG. 5comprises at least one of a plurality of pilot signals 550 withinconcurrent resource elements of received encoded symbol streams 535, andto add an extension to the demodulation reference signal 805. Asdescribed in greater detail below, the extension module 810 may extendfront and/or rear boundaries of the pilot signals' envelope in order togenerate an extended frequency domain signal within the demodulationreference signal 805.

The channel estimation module 560 further comprises inverse discreteFourier transform (IDFT) module 820, arranged to perform an IDFTfunction on the extended demodulation reference signal, in order togenerate a time domain reference signal 830. For the illustratedexample, the demodulation reference signal 805 comprises a plurality ofpilot signals located within concurrent resource elements to whichfrequency modulation has been applied. Accordingly, by performing anIDFT function on the extended demodulation reference signal 805, thepilot signal components are converted from the frequency domain into thetime domain. As a result, the pilot signal components within the timedomain reference signal 830 are effectively shifted with respect to oneanother in time.

Reference and separation module 840 of the channel estimation module 560then separates out at least one pilot signal component 850 from the timedomain reference signal 830. For example, the reference and separationmodule 840 may be arranged to sample the time domain reference signal830 over time intervals corresponding to the IDFT period, in order toretrieve a plurality of individual pilot signal components 850. Forpilot signals modulated onto frequencies other than the first discretefrequency within the Fourier spectrum for the IDFT function, thecorresponding pilot signal component 850 may, having been separated outfrom the time domain signal 830, be shifted by shift module 860 torelocate the pilot signal component 850 to a channel tap correspondingto the first sample interval within a shifted time domain referencesignal 865. For example, the shift module 860 may be arranged to performa circular shift function on the pilot signal component. Filtering ofeach separated (and where appropriate time-shifted) pilot signalcomponent may then be performed by filter module 870. Different kinds offiltering may be implemented to reduce the noise levels. For example, asimple way of eliminating noise is to ‘null’ a large amount of thechannel taps, depending upon either an amplitude threshold or thesub-carrier index, or both.

Discrete Fourier transform (DFT) module 880, is then arranged to performa DFT function on each of the at least one pilot signal components togenerate at least one extended intermediate channel estimation signal.The edges of at least one extended intermediate channel estimationsignal, which relate to the extensions added by extension circuitry 810,may then be trimmed, for example by DFT module 880 or by a separatelogical element (not shown), to generate the required channel estimationsignal 570 that is arranged to comprise substantially no edge effect.Alternatively, the channel estimation signal 570 may comprise theextended channel estimation signal 890 as generated by the DFT module880. In this manner, each pilot signal component may be transformed backfrom the time domain into the frequency domain to provide the channelestimation signal 570, which may then be provided to the equalizer 540.The equalizer 540 may then be able to use the channel estimationsignal(s) 570 to determine an impulse response for the correspondingcommunication channel(s) and to compensate for the fading nature of therespective communication channel(s) in order to more accuratelydemodulate the encoded symbols within the respective received encodedsymbol stream(s) 535.

As mentioned above, the extension module 810 extends the pilot signals'envelope to generate an extended frequency domain signal within thedemodulation reference signal 805. In this manner, the edge effectresulting from the IDFT and DFT functions and the filtering performed inthe time domain may be substantially confined to the extended regions ofthe frequency domain signal, thereby enabling the real frequency domainsignal for the sub-carrier allocations containing the pilot signals toremain substantially unaffected by any ‘edge’ effect.

FIG. 9 illustrates an example of an extension of the frequency domainsignal comprising the pilot signals within the demodulation referencesignal 805. The original (real) frequency domain signal for thesub-carrier allocations containing the pilot signals, and whichrepresents the impulse response for the communication channel(s), isillustrated at 910. In accordance with some examples of the presentinvention, the frequency domain signal 910 is extended such that theextended frequency domain signal comprises substantially nodiscontinuities in the regions around the beginning 920 or end 930 ofthe original frequency domain signal 910, in order to allow for thesettling of the pilot signal components within the frequency domainsignal during subsequent analysis thereof, and thus enabling the realfrequency domain signal for the sub-carrier allocations containing thepilot signals 910 to remain substantially unaffected by any ‘edge’effect.

Furthermore, and in accordance with the example illustrated in FIG. 9,the frequency domain signal 910 may be extended, such that an extensionapplied to the beginning of the frequency domain signal 910 and anextension applied to the end of the frequency domain signal 910 isrespectively applied at substantially the same amplitude. In thismanner, the frequency domain signal 910 may be extended such that anydiscontinuities may be substantially avoided where a beginning extensionsignal and an ending extension signal meet. As illustrated in FIG. 9,this may be achieved by estimating tangents 940 and 950 at the start andend of the real frequency domain signal 910, and then extending thetangents 940, 950 such that they meet and form a continuous curve 960.

In accordance with some examples, the received frequency domain signal,which may contain several users transmitting simultaneously, isextrapolated treating separately odd and even sub-carriers, for example.In the example of treating separately odd and even sub-carriers, each(odd or even) sub-carrier is the sum of H1 and H2. Hence, it is possibleto extrapolate (H1+H2) directly, which provides the same result asextrapolating H1, then H2, then summing all values. This operation ispossible because of the mathematical linearity of the extensioncreation, as shown in [Eq. 4].

For example, in a case where there are two transmitting devices, eachtransmitting pilot signals within resource elements comprising the samecommon time index across all sub-carrier frequencies (as illustrated inFIG. 7), even and odd sub-carriers may be treated separately. Thus, thereceived signal is the sum of two independent transmissions:

R=S ₁ H ₁ +S ₂ H ₂ +N  [Eq. 1]

where S₁ and S₂ represent the transmitted sequences of the first andsecond transmitting devices respectively, and H₁ and H₂ represent thecommunication channels for the first and second transmitting devicesrespectively. Both S₁ and S₂ may share the same DMRS sequence root; onesequence being shifted compared to the other, so that the channel tapsmay be separated in the time domain after the IDFT function isperformed. For example, where there are two transmitted sequences, eachtransmitter transmits the same known sequence (e.g. a known referencesignal multiplied by a pilot sequence, such as a Zadoff-Chu or CAZACsequence), but with the two sequences being time shifted relative to oneanother. This shift in the time domain may be half the allocation size,allowing best separation of the taps. Such a circular shift in the timedomain translates in a phase rotation in the frequency domain as:

e ^(iΠ*0)=+1; e ^(iΠ*1)=−1  [Eq. 2]

Thus, where N_(—) _(sc) is the number of sub-carriers in the allocation:

$\begin{matrix}{S_{1} = {{\begin{bmatrix}S_{11} \\S_{12} \\S_{13} \\S_{14} \\\ldots \\S_{1\; {N\_ sc}}\end{bmatrix}\mspace{14mu} {and}\mspace{14mu} S_{2}} = {\begin{bmatrix}S_{21} \\S_{22} \\S_{23} \\S_{24} \\\ldots \\S_{2\; {N\_ sc}}\end{bmatrix} = \begin{bmatrix}{+ S_{11}} \\{- S_{12}} \\{+ S_{13}} \\{- S_{14}} \\\ldots \\{- S_{1\; {N\_ sc}}}\end{bmatrix}}}} & \left\lbrack {{Eq}.\mspace{14mu} 3} \right\rbrack\end{matrix}$

and the received signal at the receive antenna (R) multiplied by theconjugate of the reference sequence (S₁) y may be given by:

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\y_{3} \\y_{4} \\\ldots \\y_{N\_ sc}\end{bmatrix} = {{R*\overset{\_}{S_{1}}} = {\begin{bmatrix}{H_{11} + H_{21}} \\{H_{12} - H_{22}} \\{H_{13} + H_{23}} \\{H_{14} - H_{24}} \\\ldots \\{H_{1{N\_ sc}} - H_{2\; {N\_ sc}}}\end{bmatrix} + {N*\overset{\_}{S_{1}}}}}}} & \left\lbrack {{Eq}.\mspace{14mu} 4} \right\rbrack\end{matrix}$

FIG. 10 illustrates the frequency domain view of the pilot signals. Ascan be seen, y is split between even and odd data streams, the odd datastream corresponding to sub-carriers where y_(x)=S_(2x)+S_(1x), and theeven data stream corresponding to sub-carriers wherey_(x)=S_(2x)+S_(1x), x being the sub-carrier index.

The odd and even streams of the demodulation reference signal y can beextrapolated separately to determine extensions for each of the separatepilot signals, as illustrated in FIG. 11, and then each of theextrapolated odd and even streams may be re-mixed and appended to theinitial demodulation reference signal y.

Referring now to FIG. 12 there is illustrated an example of Mean SquareError (MSE) plots for a traditional frequency domain channel estimationapproach 1210, a traditional DFT based channel estimation approach 1220and a DFT based channel estimation approach 1230. As can be seen, whilstthe traditional DFT based channel estimation approach 1220 performsadequately within the central region of the allocation, the MSE at eachedge of the plot for the traditional DFT based channel estimationapproach 1220 is very poor, and significantly worse than that for thetraditional frequency domain channel estimation approach 1210. However,the DFT based channel estimation approach according to the illustratedexample 1230 not only performs adequately within the central region ofthe allocation, but also performs as well as the traditional frequencydomain channel estimation approach 1210 at the edges, but without thecomplexity and costs associated with the frequency domain channelestimation approach.

Referring now to FIG. 13, there is illustrated an example of asimplified flowchart 1300 of a method for generating a channelestimation signal based on at least one of a plurality of pilot signalswithin concurrent resource elements. The method starts and moves to step1310 with the receipt of a demodulation reference signal comprising aplurality of pilot signals. Next, in step 1315, the received referencesignal is multiplied by the conjugate of the reference sequence. Themethod then moves on to step 1320, where extensions are added to themultiplied demodulation reference signal. An IDFT function is thenperformed in order on the extended demodulation reference signal togenerate a time domain reference signal, in step 1330. The method thenmoves on to step 1340, where channel tap separation is performed toseparate out at least one pilot signal component from the time domainreference signal. Next, in step 1350, if necessary, a circular shift isapplied to the separated pilot signal component(s) within the timedomain. Thereafter, in step 1360, filtering of the separated pilotsignal component(s) is performed, also within the time domain, togenerate an intermediate signal. A DFT function is then performed on theintermediate signal comprising the pilot signal component to transformit from the time domain into an extended channel estimation signalwithin the frequency domain, in step 1370. The intermediate signal isthen trimmed to generate a channel estimation signal in step 1380, andthe method then ends.

Accordingly, the examples of a method and apparatus hereinbeforedescribed enable the generation of a channel estimation signal for acommunication channel based on a demodulation reference signalcomprising a plurality frequency division multiplexed pilot signalsusing IDFT functions and DFT functions, within the channel estimationprocess, thus enabling a simplified channel estimation circuit design,whilst substantially alleviating the problem of high Mean Square Error(MSE) at the edges of the channel estimation allocation when transformedback into the frequency domain.

In the foregoing specification, the invention has been described withreference to specific examples of embodiments of the invention. It will,however, be evident that various modifications and changes may be madetherein without departing from the broader scope of the invention as setforth in the appended claims. For example, the connections may be anytype of connection suitable to transfer signals from or to therespective nodes, units or devices, for example via intermediatedevices. Accordingly, unless implied or stated otherwise the connectionsmay for example be direct connections or indirect connections.

The conductors as discussed herein may be illustrated or described inreference to being a single conductor, a plurality of conductors,unidirectional conductors, or bidirectional conductors. However,different embodiments may vary the implementation of the conductors. Forexample, separate unidirectional conductors may be used rather thanbidirectional conductors and vice versa. Also, plurality of conductorsmay be replaced with a single conductor that transfers multiple signalsserially or in a time multiplexed manner. Likewise, single conductorscarrying multiple signals may be separated out into various differentconductors carrying subsets of these signals. Therefore, many optionsexist for transferring signals.

Because the apparatus implementing the present invention is, for themost part, composed of electronic components and circuits known to thoseskilled in the art, circuit details will not be explained in any greaterextent than that considered necessary as illustrated above, for theunderstanding and appreciation of the underlying concepts of the presentinvention and in order not to obfuscate or distract from the teachingsof the present invention.

Although the invention has been described with respect to specificconductivity types or polarity of potentials, skilled artisansappreciated that conductivity types and polarities of potentials may bereversed.

Moreover, the terms “front,” “rear,” “top,” “bottom,” “over,” “under”and the like in the description and in the claims, if any, are used fordescriptive purposes and not necessarily for describing permanentrelative positions. It is understood that the terms so used areinterchangeable under appropriate circumstances such that theembodiments of the invention described herein are, for example, capableof operation in other orientations than those illustrated or otherwisedescribed herein.

Thus, it is to be understood that the architectures depicted herein aremerely exemplary, and that in fact many other architectures can beimplemented that may substantially achieve the same functionality. In anabstract, but still definite sense, any arrangement of components toachieve the same functionality is effectively “associated” such that thedesired functionality is achieved. Hence, any two components hereincombined to achieve a particular functionality can be seen as“associated with” each other such that the desired functionality isachieved, irrespective of architectures or intermediary components.Likewise, any two components so associated can also be viewed as being“operably connected,” or “operably coupled,” to each other to achievethe desired functionality.

Furthermore, those skilled in the art will recognize that boundariesbetween the functionality of the above described operations merelyillustrative. The functionality of multiple operations may be combinedinto a single operation, and/or the functionality of a single operationmay be distributed in additional operations. Moreover, alternativeembodiments may include multiple instances of a particular operation,and the order of operations may be altered in various other embodiments.

Also, the invention is not limited to physical devices or unitsimplemented in non-programmable hardware but can also be applied inprogrammable devices or units able to perform the desired devicefunctions by operating in accordance with suitable program code.Furthermore, the devices may be physically distributed over a number ofapparatuses, while functionally operating as a single device. Also,devices functionally forming separate devices may be integrated in asingle physical device.

However, other modifications, variations and alternatives are alsopossible. The specifications and drawings are, accordingly, to beregarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other elements or steps then those listed in aclaim. Furthermore, Furthermore, the terms “a” or “an,” as used herein,are defined as one or more than one. Also, the use of introductoryphrases such as “at least one” and “one or more” in the claims shouldnot be construed to imply that the introduction of another claim elementby the indefinite articles “a” or “an” limits any particular claimcontaining such introduced claim element to inventions containing onlyone such element, even when the same claim includes the introductoryphrases “one or more” or “at least one” and indefinite articles such as“a” or “an.” The same holds true for the use of definite articles.Unless stated otherwise, terms such as “first” and “second” are used toarbitrarily distinguish between the elements such terms describe. Thus,these terms are not necessarily intended to indicate temporal or otherprioritization of such elements. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

1. An integrated circuit comprising: a channel estimation moduleconfigured to generate at least one channel estimation signal based onat least one of a plurality of pilot signals within concurrent resourceelements, wherein the channel estimation module comprises: an extensionmodule arranged to receive a demodulation reference signal comprisingthe plurality of pilot signals, and add an extension to the demodulationreference signal, an inverse discrete Fourier transform (IDFT) modulearranged to perform an inverse discrete Fourier transform function onthe extended demodulation reference signal to generate a time domainreference signal, a reference signal separation module arranged toseparate out at least one pilot signal component from the time domainreference signal, and a discrete Fourier transform module arranged toperform a discrete Fourier transform function on the at least one pilotsignal component to generate at least one extended channel estimationsignal.
 2. The integrated circuit of claim 1 wherein the DFT module isfurther arranged to trim at least one edge of the at least one extendedchannel estimation signal in order to generate the channel estimationsignal.
 3. The integrated circuit of claim 1 wherein the extensionmodule is further arranged to extend a frequency domain signal of thereceived demodulation reference signal comprising the pilot signals,such that at least one of the following is achieved: the frequencydomain signal is extended to a length of a power of two; the extendedfrequency domain signal comprises no discontinuities in a region arounda beginning or an end of the original frequency domain signal; and anextension applied to a beginning of the frequency domain signal and anextension applied to the end of the frequency domain signal start andend respectively at a same amplitude.
 4. The integrated circuit of claim1 wherein the extension module is further arranged to: determine atleast one extension for separate frequency domain signals for the pilotsignals individually, and sum extensions for separate frequency domainsignals to generate an overall extension for the demodulation referencesignal.
 5. The integrated circuit of claim 4 wherein the extensionmodule is further arranged to: separately extrapolate odd and evenstreams of the demodulation reference signal to determine a plurality ofextensions for separate pilot signals, and remix and append theextrapolated odd and even streams to the demodulation reference signal.6. The integrated circuit of claim 1 wherein the plurality of pilotsignals are based on a known reference symbol multiplied by a knownpilot sequence.
 7. The integrated circuit of claim 6 wherein theextension module is further arranged to multiply the receiveddemodulation reference signal by a conjugate of the pilot sequence priorto said adding the extension to the demodulation reference signal. 8.The integrated circuit of claim 6 wherein the pilot sequence comprisesone of a Zadoff-Chu or constant amplitude zero autocorrelation waveformsequence.
 9. The integrated circuit of claim 1 wherein the channelestimation module further comprises a shift module arranged to perform acircular shift function on the at least one pilot signal componentseparated out from the time domain reference signal.
 10. The integratedcircuit of claim 1 wherein the channel estimation module furthercomprises: a filter module arranged to filter the at least one pilotsignal component separated out from the time domain reference signal.11. The integrated circuit of claim 1 wherein the channel estimationmodule is adapted for use within a receiver chain module configured toreceive data within an orthogonal frequency division multiplexing (OFDM)communication system.
 12. The integrated circuit of claim 1 wherein thechannel estimation module is adapted for use within a receiver chainmodule configured to receive data within a multiple input multipleoutput (MIMO) communication system.
 13. A communication unit comprisingthe integrated circuit of claim
 1. 14. A method for generating a channelestimation signal, the method comprising: receiving a demodulationreference signal comprising a plurality of pilot signals; adding anextension to the demodulation reference signal to generate an extendeddemodulation reference signal; performing an inverse discrete Fouriertransform (IDFT) function on the extended demodulation reference signalto generate a time domain reference signal; separating out at least onepilot signal component from the time domain reference signal; andperforming a discrete Fourier transform (DFT) function on the at leastone pilot signal component to generate at least one extended channelestimation signal.
 15. The method of claim 14 further comprising:trimming at least one edge of the at least one extended channelestimation signal to generate the channel estimation signal.
 16. Themethod of claim 14 further comprising: extending a frequency domainsignal of the demodulation reference signal, wherein said extending thefrequency domain signal provides one or more of the frequency domainsignal is extended to a length of a power of two, the extended frequencydomain signal comprises no discontinuities in a region around abeginning or an end of the original frequency domain signal, and anextension applied to the beginning of the frequency domain signal and anextension applied to the end of the frequency domain signal start andend respectively at a same amplitude.
 17. The method of claim 14 furthercomprising: determining at least one extension for separate frequencydomain signals for the pilot signals individually; and generating anoverall extension for the demodulation reference signal by summingextensions for separate frequency domain signals.
 18. The method ofclaim 17 further comprising: determining a plurality of extensions forseparate pilot signals, wherein said determining the plurality ofextensions comprises separately extrapolating odd and even streams ofthe demodulation reference signal; and remixing and appending theextrapolated odd and even streams to the demodulation reference signal.19. The method of claim 14 further comprising: performing a circularshift function on the at least one pilot signal component separated outfrom the time domain reference signal.
 20. The method of claim 14further comprising: filtering the at least one pilot signal componentseparated out from the time domain reference signal.